Field of the Invention
The present invention relates to a liquid ejection head substrate, a method of manufacturing the same, and a method of processing a silicon substrate to form a through-hole in the silicon substrate.
Description of the Related Art
One of liquid ejection heads ejecting liquids is a type of liquid ejection head which includes an ejection energy-generating element placed on a surface of a substrate and which ejects liquid in a normal direction of the substrate surface. This type of liquid ejection head is referred to as a side shooter-type head. A substrate having an ejection energy-generating element placed on a surface thereof is referred to as a liquid ejection head substrate. A side shooter-type head is used as, for example, an inkjet printhead that ejects ink, which is liquid, to make a record on a recording medium such as a recording sheet. In the side shooter-type head, a silicon substrate made of single-crystalline silicon is usually used as a liquid ejection head substrate. In descriptions below, a surface of a liquid ejection head substrate that has an ejection energy-generating element placed thereon is referred to as a first surface and a surface of the liquid ejection head substrate that is on the back side of the first surface is referred to as a second surface. In the side shooter-type head, a through-hole is formed in the silicon substrate, which is a liquid ejection head substrate, and is used as a supply path and liquid is supplied to the position of an ejection energy-generating element placed on a first surface of the silicon substrate from the second surface side of the silicon substrate through the supply path. The supply path is formed in such a manner that, for example, a second surface of the silicon substrate is etched.
Japanese Patent Laid-Open No. 10-181032 discloses an example of a method of manufacturing a side shooter-type head configured as an inkjet printhead. In the method, in order to suppress the variation in opening diameter of supply paths in a first surface of a silicon substrate which is a liquid ejection head substrate, sacrificial layers are placed on the first surface such that a substrate material can be selectively etched depending on the positions of through-holes for forming supply paths. Therefore, the supply paths are formed so as to have a predetermined opening diameter depending on the size of each sacrificial layer.
U.S. Pat. No. 6,805,432 discloses a method of manufacturing an inkjet printhead using a silicon substrate having a surface of which the plane indices are (100) as a liquid ejection head substrate. In the method disclosed in U.S. Pat. No. 6,805,432, after the silicon substrate is dry-etched using an etching mask layer placed on a second surface of the silicon substrate, the silicon substrate is further anisotropically etched using the same etching mask layer. During dry etching, holes are formed by etching so as not extend through the silicon substrate. The holes are then processed into through-holes by anisotropic etching. This allows a liquid ejection head substrate having supply paths formed from the through-holes to be obtained. The supply paths have such a cross-sectional shape that an intermediate portion laterally expands.
In the method disclosed in U.S. Pat. No. 6,805,432, dry etching and anisotropic etching, that is, wet etching both use the same etching mask layer. Therefore, the opening width of the supply paths in the second surface is determined depending on the opening width of the etching mask layer placed on the second surface of the silicon substrate and the amount of engraving by dry etching. Incidentally, in a configuration in which supply paths having slit-shaped openings extending in one direction are arranged in an elongated substrate and a plurality of ejection energy-generating elements are arranged along the openings, the term “opening width” as used herein refers to the lateral opening width of the openings of the supply paths that extend in one direction. A lateral direction of the openings of the supply paths that extend in one direction is defined as a width direction of a liquid ejection head. In the case of using the liquid ejection head as an inkjet printhead, a plurality of ejection energy-generating elements are usually arranged along openings of supply paths that extend in one direction. In the method disclosed in U.S. Pat. No. 6,805,432, a silicon (111) plane which has a relatively low etching rate and which is inclined at 54.7° to a (100) plane is formed using the anisotropic etching of silicon and supply paths are open to a first surface. Therefore, in order to increase the opening width of the supply paths in the first surface to a certain extent, the amount of engraving by dry etching needs to be increased. However, as the amount of engraving is increased, the time taken for dry etching is increased. Hence, production efficiency may possibly be reduced.
Japanese Patent Laid-Open No. 2004-148824 discloses a method of manufacturing an inkjet printhead by forming supply paths in a silicon substrate. The supply paths are formed in such a manner that after the silicon substrate is laser-trenched, the silicon substrate is etched. In this method, the amount of engraving by laser processing needs to be increased so as to be substantially comparable to the thickness of the silicon substrate. However, as the amount of engraving by laser processing is increased, the time taken for laser processing is increased. Hence, production efficiency may possibly be reduced.
Japanese Patent Laid-Open No. 2007-237515 discloses a method of manufacturing a liquid ejection head substrate and describes that supply paths are formed in such a manner that non-through holes are formed in a silicon substrate using a laser beam and the silicon substrate is then anisotropically etched. In this method, the supply paths are formed so as to have such a cross-sectional shape that an intermediate portion is laterally wide and therefore there is a limitation in reducing the lateral size of a liquid ejection head.
In a step of assembling the liquid ejection head, the liquid ejection head substrate is mounted on a support member. The support member supports the liquid ejection head substrate and has a liquid channel for supplying liquid to the supply paths from a tank or the like. The liquid ejection head substrate is mounted on the support member in such a manner that, for example, an ultraviolet/heat-curable adhesive is transferred or applied to a surface of the support member and the liquid ejection head substrate is precisely aligned with the support member and is then pressed against the support member. In this operation, a second surface of the liquid ejection head substrate is brought into contact with the support member. For example, image processing or the like is used for precise alignment. An ultraviolet ray is applied to the adhesive that extends on a peripheral portion of the liquid ejection head substrate, which is pressed against the support member, whereby the liquid ejection head substrate is temporarily fixed to the support member. In this operation, a region interposed between the liquid ejection head substrate and the support member is hidden from the ultraviolet ray and therefore a portion of the adhesive that is present in the region interposed between the liquid ejection head substrate and the support member remains uncured. Thereafter, a heat-curing step is performed, whereby the adhesive including the portion present in the region interposed between the liquid ejection head substrate and the support member is cured.
In the above assembling step, when the liquid ejection head substrate is pressed against the support member having the adhesive transferred or applied thereto, the uncured adhesive is squeezed into the supply paths because the supply paths are open to the second surface of the liquid ejection head substrate in this point of time. The adhesive squeezed into the supply paths is thereafter cured in the heat-curing step. When the cured adhesive squeezed into the supply paths is present in narrow portions of the supply paths, the flow of liquid in the supply paths is interrupted. In particular, when liquid flowing in the supply path contains bubbles, the bubbles are blocked in the narrow portions of the supply paths by the cured adhesive and grow to significantly interrupt the flow of the liquid. When liquid contains bubbles, the ease of discharging the bubbles from supply paths together with the liquid is referred to as bubble releasability. In liquid ejection head substrates, supply paths with good bubble releasability need to be arranged. Japanese Patent Laid-Open Nos. 11-348282 and 2001-162802 disclose an inkjet printhead manufactured by bonding a plurality of substrates with an adhesive. In the inkjet printhead, in order to prevent the adhesive from flowing into an ink channel, an excess of the adhesive is stored in an adhesive storage region formed in a surface of each substrate. However, even if an adhesive storage region such as a recessed portion or a groove is formed in a surface of a substrate, an adhesive cannot be sufficiently prevented from being squeezed into a supply path. In a liquid ejection head, a surface of a liquid ejection head substrate is required to be not inclined to a surface of a support member and therefore the liquid ejection head substrate needs to be pressed against the support member. An adhesive is necessarily squeezed into a supply path by pressing the liquid ejection head against the support member. The amount of the squeezed adhesive is reduced in such a manner that the amount or state of the adhesive is regulated when the adhesive is transferred or applied. However, the standard width of a region to which the adhesive is transferred or applied is very small in terms of manufacture and therefore very difficult control is required during manufacture.